Method for recycling pulp rejects

ABSTRACT

The present invention relates to a process for recycling cleaner rejects from the preparation of paper, paperboard and cardboard and to their use for the preparation of paper in the paper stock or as a coating slurry for the paper industry.

[0001] The present invention relates to a process for recycling cleanerrejects from the preparation of paper, paperboard and cardboard and totheir use for the preparation of paper in the paper stock or as acoating slurry for the paper industry.

[0002] In the preparation of paper, the raw material, i.e., wood pulp,wood, fine straw pulp or rag pulp, is also admixed with repulpedhalf-stock, fillers and pigments in order to achieve a closed surfaceand thus to improve the properties of the paper, especially thewhiteness, opacity and printability.

[0003] Almost all papers are admixed with fillers which confer a uniformformation, improved softness, whiteness and touch especially to printingand writing papers. These fillers, mostly called “ashes” since theyremain as ashes in the combustion analysis, are either added to thefiber suspension or applied in the coating step.

[0004] Uncoated papers contain up to 35% by weight of fillers, coatedpapers contain from 25 to 50% by weight thereof. The amount of fillersemployed is highly dependent on the intended use of the paper. Highlyfilled papers have a lower strength and poorer sizing properties.

[0005] The filler content in the paper stock is usually between 5 and35% by weight and consists of primary pigments or recycled coatingpigments which may be derived from coating residuals or from coatedrejects. In addition to the whiteness of the filler which is importantfor whitened papers, its grain size plays an important role since it hasa strong influence on the filler efficiency and the physical propertiesof the paper, in particular porosity. The proportion of filler remainingin the paper is between 20 and 80% of the amount added to the fibersuspension.

[0006] As judged by their consumption, the following products haverather great importance today as fillers and coating pigments: chinaclay, calcium carbonate, precipitated calcium carbonate (PCC),artificial aluminum silicates and oxide hydrates, titanium dioxide,satin white, talcum and calcium silicate.

[0007] Subsequently to their coating with coating slurries, papers areoften smoothed, after drying, with a blade. The so-called cleanerrejects obtained therein, also referred to as coated rejects, mainlyconsist of minerals and fibers and may comprise from 1 to 4% of thetotal volume of the paper produced. In most cases, they are disposed ofin dumps. Thus, for example, it has been proposed to compress andcompact the cleaner rejects by screw extruders in order to reduce theirvolume. However, the total amount of the cleaner rejects obtained andpassed to disposal is not reduced.

[0008] In the past, another possibility of treating the cleaner rejectswas to partly process them using centrifugal cleaners in order toseparate the fibers, on the one hand, and/or the coating pigments andfillers, on the other hand, and reuse them at least in part.

[0009] It is the object of the present invention to provide a newenvironmentally friendly concept for treating the cleaner rejects,especially from centrifugal cleaners, and to enable them to be recycledas completely as possible.

[0010] In particular, the object of the invention is to provide aprocess for the recycling of cleaner rejects while energy costs andcosts of raw materials, shipping costs as well as costs for dumping aresaved.

[0011] According to the invention, the above object is achieved by aprocess for recycling cleaner rejects, especially from centrifugalcleaners, from the preparation of paper, paperboard and cardboard,characterized in that cleaner rejects, which contain fibers, coatingpigments and/or fillers, are milled to the desired grain sizedistribution, optionally with the addition of water, coating pigment,fresh filler and/or filler slurry, and employed as a raw material forthe paper stock and/or coating slurry.

[0012] The cleaner rejects, which are usually solid, contain valuableraw materials which can be recovered by means of the present inventionand, after milling, recycled to various processes of papermaking.Especially the cleaner rejects from paper mills which prepare coatedpaper or cardboard grades contain large quantities of coating pigmentflakes. The thicker the coating layer, the more difficult is therecovery of the flakes by the prior art technologies. Double-coatedgrades or coated cardboard grades may be mentioned here as particularexamples. Another group of paper industries are the SC-paper producingplants, which lose large amounts of fillers through cleaner rejects.

[0013] Now, by means of the present invention, the cleaner rejects aremilled and optionally admixed with water, coating pigment, filler and/orfiller slurry. The cleaner reject slurry or the milled powder is thenrecycled to the papermaking process for the paper stock and/or as acoating slurry.

[0014] On a closer inspection of the cleaner rejects, fractions offillers, coating pigment flakes, fiber suspension residuals, such asfiber lumps or splinters, as well as foreign matter, for example, sand,can be discovered.

[0015] After the milling of the cleaner rejects, the distribution of theparticle sizes of the cleaner rejects is essentially the same as theoriginal distribution in the coating pigments, fillers or filler/pigmentslurries. Thus, at the same time, by means of the present invention,more than 95% of the total cleaner rejects, or even the full amountthereof, can be recovered and recycled to production.

[0016] Then, the cleaner rejects processed according to the inventionserves, for example, as a filler, whereby the consumption of freshfiller or pigment can be reduced consistently.

[0017] According to the invention, the milling of the cleaner rejects ispreferably installed in a centrifugal cleaner system downstream from thelast of usually several stages of a centrifugal cleaner. The acceptedstock from the additional cleaner system is recycled to the previousstage, and the residual amount of the cleaner rejects forms the finalreject.

[0018] In an existing cleaner system, the simplest application area isintended to comprise installing the milling after the last but onecleaner stage and employing the last cleaner process as a final stage.

[0019] When the process according to the invention was performed, it wasfound that the distribution of particle sizes of the coating pigmentflakes had been refined and that the original distribution of thepigment particles had been achieved. This could be seen from thequantity of finer particles, especially in the differentialdistribution. The fiber knots were extracted and predominantly refined.

[0020] In papermaking, it is usual to employ the fillers and coatingpigments either as powders or in the form of concentrated slurries witha solids content of preferably from 30 to 85% by weight for the paperstock or for the preparation of coating slurries. The fresh fillers andpigments are usually supplied by the manufacturers with the desiredwhiteness and grain size distribution as a slurry or powder.

[0021] In the processing of cleaner rejects, it is of course required toseparate and discard the coarse dirt contents consisting of splinters,sand grains and other impurities. For this purpose, multistagecentrifugal cleaners are usually employed. The screenings thus obtainedconsist of fibers, fillers, pigments, fine sand, black particles andagglomerates of fillers and pigments, or pigments, fibers and fillers.“Filler” usually means the fine particles employed in the paper stock;“pigment” means the fine particles employed in the coat.

[0022] Known methods which suggest themselves for the separation of theundesirable contents of the cleaner rejects are flocculation andsedimentation, filtering, screening and/or centrifuging. In this case, amixture of different pigments is usually present which often containschina clay, calcium carbonate and talcum. Agglomerates frequently formduring the separation processes due to flocculation and charge reversal;they can now be milled according to the invention.

[0023] According to the invention, the milling into powders or slurriescan be performed continuously or discontinuously in usual dry mills orwet mills, especially agitator ball mills, for example, having a contentof from 700 to 5000 l or more. Milling media, preferably milling balls,especially having a diameter of from 1 to 4 mm, are used.

[0024] Screens, preferably sieve bends, for separating impurities (ballcrushings, separating materials, rust etc.) are usually used forprocessing. Laser measuring instruments serve to determine and controlthe milling fineness during the milling process and for thecomputer-based control of the agitator ball mill system.

[0025] Therefore, for the preparation of new coating slurries or also,optionally, for use in the paper stock, it may be required to enhancethe whiteness by per se known methods. The disruption of agglomerateswhich adversely affect the flowing properties of a coating slurry at theblade by forming doctor streaks and adversely affect the properties ofthe coat is particularly preferred. Dispersing aids, fillers andpigments additionally employed in the milling process reduce the overallconsumption of these materials.

[0026] In the cleaner rejects, the ratio of fillers and/or pigments tofibers can vary widely. It is particularly preferred according to theinvention to employ cleaner rejects having an optionally enrichedconcentration of fillers and/or coating pigments within a range of from5 to 90% by weight, especially from 30 to 70% by weight, based on thesolids content. Thus, the fiber content, on the one hand, or the contentof filler and/or coating pigment may vary, for example, from 1 to 99% byweight, or from 99 to 1% by weight. “Enrichment” within the meaning ofthe present invention especially comprises the addition of fresh fillerand/or fresh pigment.

[0027] Therefore, according to the present invention, china clay,natural or precipitated calcium carbonates, artificial or naturalaluminum silicates and oxide hydrates, titanium dioxide, satin white,dolomite, mica, metal flakes, especially aluminum flakes, bentonite,rutile, magnesium hydroxide, gypsum, sheet silicates, talcum, calciumsilicate and other rocks and earths are preferably used as the freshpigment and/or fresh filler before, after and/or during the milling.

[0028] The fresh pigment or fresh filler is preferably employed as apowder, aqueous fresh-pigment containing and/or fresh-filler containingslurries in the presence of the cleaner rejects and optionally usualmilling aids and/or dispersing aids to give a slurry with a solidscontent of, for example, from 30 to 85% by weight, especially from 40 to75% by weight.

[0029] Preferably, the added amount of fibers, coating pigments and/orfillers (recycled or fresh) is from 1 to 100% by weight, based on thecleaner rejects.

[0030] Particularly preferred is the addition of water in order toemploy the cleaner rejects milled according to the invention in adiluted slurry for the stock flow. Slurries having a solids content offrom 5 to 50% by weight, especially from 10 to 20% by weight, arepreferably employed. Accordingly, in a preferred embodiment according tothe invention, the milling is performed in the presence of water in anamount of from 1 to 1000% by weight, especially from 100 to 1000% byweight, based on the solids content.

[0031] The cleaner rejects are preferably milled to a slurry or powderhaving a grain size distribution of from 10 to 99% by weight ofparticles <1 μm, especially from 10 to 95% by weight of particles <1 μm,respectively based on the equivalent diameter.

[0032] From EP 0 625 611 A1, grain size distributions for coatingpigments are known which are also preferably adjusted by means of thepresent invention. Thus, it is particularly preferred according to thepresent invention for the pigments to have the following grain sizedistribution:

[0033] a) from 95 to 100% by weight of particles <10 μm;

[0034] b) from 50 to 100% by weight of particles <2 μm, especially from50 to 95% by weight of particles <2 μm;

[0035] c) from 27 to 95% by weight of particles <1 μm, especially from27 to 75% by weight of particles <1 μm; and

[0036] d) from 0.1 to 55% by weight of particles <0.2 μm, especiallyfrom 0.1 to 35% by weight of particles <0.2 μm;

[0037] respectively based on the equivalent diameter of the particles.

[0038] In addition, according to the invention, a broad variation of thewhiteness and grain size distributions is possible, which can becontrolled, in particular, by the manner and duration of milling. Thus,it is possible to mix a relatively coarse fresh filler and water in situwith a large amount of cleaner rejects for introducing this slurry intothe paper stock after milling. In the same way, it is possible to use asmaller amount of cleaner rejects and to perform a finer milling withfresh pigment in situ which is then used as a coating pigment,especially in precoating.

[0039] Even though per se known wetting agents, stabilizers, millingaids and dispersing aids may be employed according to the inventionduring the mixing and milling of the cleaner rejects, as known, forexample, from EP 0 625 611 A1, the quantity thereof required is clearlyreduced according to the invention as compared to the prior art. Thecleaner rejects already contain some amount of the mentioned agentswhich are recycled to the papermaking process according to theinvention.

[0040] The powders or slurries obtainable according to the presentinvention may be employed to particular advantage in the paper industry,especially for the preparation of a coat for paper coating or in thepaper stock. When the fiber content is low, the cleaner rejects milledaccording to the invention is preferably employed in the coating slurry,and when the fiber content is high, it is preferably employed in thepaper stock. According to the invention, a good retention on the screenis obtained. Particularly preferred is the use of the cleaner rejectsmilled according to the invention for the preparation of offset paper.In addition, the slurries according to the invention are also suitablefor the preparation of a coating slurry for light-weight coated papers,especially with high coating speeds, and for the preparation of rotaryoffset papers, especially for the preparation of light-weight coatedrotary offset papers, the coating of cardboard and special papers, suchas labels, wallpapers, silicone base paper, self-copying paper, and foradmixture with intaglio printing paper. Thus, the coating pigmentslurries obtainable according to the invention may be employed, inparticular, in sheet-fed offset papers, especially for sheet-fed offsetsingle coating, sheet-fed offset double coating: sheet-fed offsetprecoating and sheet-fed offset top coating; in rotary offset papers,especially for LWC rotary offset single coating, rotary offset doublecoating: rotary offset precoating and rotary offset top coating; inintaglio printing, especially for LWC intaglio single coating, intagliodouble coating: intaglio precoating and intaglio top coating; incardboard, especially for cardboard double coating: cardboard precoatingand cardboard top coating; and for special papers, especially for labelsand flexible packings.

[0041] The process offers the opportunity to employ the pigment slurriesprepared according to the invention without a loss in quality in thebase papers, coatings and especially final qualities prepared therewith.

[0042] In the following, some coating formulations which can be obtainedaccording to the present invention are given for illustrative purposes(all figures converted to weight parts of solids (atro/activeingredient)). The amounts of fillers and/or pigment slurries can bepartly or wholly replaced by corresponding amounts of cleaner rejectsmilled according to the invention.

[0043] 1. Sheet-Fed Offset Paper

[0044] 1.1 Sheet-Fed Offset Single Coating

[0045] 70 parts by weight of commercially available CaCO₃ (type 90)

[0046] 30 parts by weight of commercially available clay (fine, e.g.,U.S. No. 1)

[0047] 11 parts by weight of commercially available latex (acrylate)

[0048] 0.6 parts by weight of commercially availablecarboxymethylcellulose (CMC)

[0049] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0050] 0.5 parts by weight of commercially available brightener (opt.)

[0051] 0.5 parts by weight of commercially available Ca stearate solidscontent: 64% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 8.5

[0052] 1.2 Sheet-Fed Offset Double Coating

[0053] 1.2.1 Sheet-Fed Offset Precoating

[0054] 100 parts by weight of commercially available CaCO₃ (type 60 or75)

[0055] 10 parts by weight of commercially available latex

[0056] 4 parts by weight of commercially available starch (native,oxidized, corn or potato starch)

[0057] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0058] 0.5 parts by weight of commercially available brightener (opt.)solids content: 66% Brookfield viscosity (100/min): 1,100 mPa · s pHvalue: 9.0

[0059] 1.2.2 Sheet-Fed Offset Top Coating

[0060] 70 parts by weight of commercially available CaCO₃ (type 90)

[0061] 30 parts by weight of commercially available clay (fine, e.g.;U.S. No. 1)

[0062] 10 parts by weight of commercially available latex (acrylate)

[0063] 0.6 parts by weight of commercially available CMC

[0064] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0065] 0.5 parts by weight of commercially available brightener (opt.)

[0066] 0.7 parts by weight of commercially available Ca stearate solidscontent: 64% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 8.5

[0067] 2. Rotary Offset Paper

[0068] 2.1 LWC Rotary Offset Single Coating

[0069] 50 parts by weight of commercially available CaCO₃ (type 90)

[0070] 50 parts by weight of commercially available clay (fine, Engl.clay)

[0071] 2 parts by weight of commercially available starch (native,oxidized, corn or potato starch)

[0072] 12 parts by weight of commercially available latex (XSB)

[0073] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0074] 0.7 parts by weight of commercially available brightener (opt.)

[0075] 0.5 parts by weight of commercially available Ca stearate solidscontent: 62% Brookfield viscosity (100/min): 1,400 mPa · s pH value: 8.5

[0076] 2.2 Rotary Offset Double Coating

[0077] 2.2.1 Rotary Offset Precoating

[0078] 100 parts by weight of commercially available CaCO₃ (type 60 or75)

[0079] 4 parts by weight of commercially available starch (native,oxidized, corn or potato starch)

[0080] 12 parts by weight of commercially available latex (XSB)

[0081] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0082] 0.5 parts by weight of commercially available brightener (opt.)solids content: 66% Brookfield viscosity (100/min): 1,200 mPa · s pHvalue: 9.0

[0083] 2.2.2 Rotary Offset Ton Coating

[0084] 60 parts by weight of commercially available CaCO₃ (type 95)

[0085] 40 parts by weight of commercially available clay (fine, Engl.clay)

[0086] 10 parts by weight of commercially available latex (XSB)

[0087] 0.6 parts by weight of commercially available CMC

[0088] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0089] 0.5 parts by weight of commercially available brightener (opt.)

[0090] 0.5 parts by weight of commercially available Ca stearate solidscontent: 64% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 8.5

[0091] 3. Intaglio Printing Paper

[0092] 3.1 LWC Intaglio Single Coating

[0093] 70 parts by weight of commercially available clay (normal, Engl.clay)

[0094] 30 parts by weight of commercially available talcum

[0095] 5.0 parts by weight of commercially available latex (acrylatesole binder)

[0096] 0.2 parts by weight of commercially available thickener(synthetic)

[0097] 1.0 parts by weight of commercially available Ca stearate solidscontent: 58% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 8.5

[0098] 3.2 Intaglio Double Coating

[0099] 3.2.1 Intaglio Precoating

[0100] 100 parts by weight of commercially available CaCO₃ (type 75)

[0101] 6.0 parts by weight of commercially available latex (acrylatesole binder)

[0102] 0.3 parts by weight of commercially available thickener(synthetic)

[0103] 0.5 parts by weight of commercially available Ca stearate solidscontent: 66% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 9.0

[0104] 3.2.2 Intaglio Top Coating

[0105] 85 parts by weight of commercially available clay (Engl. clay)

[0106] 15 parts by weight of commercially available clay (calcined clay)

[0107] 5.0 parts by weight of commercially available latex (acrylatesole binder)

[0108] 0.2 parts by weight of commercially available thickener(synthetic)

[0109] 0.8 parts by weight of commercially available Ca stearate solidscontent: 57% Brookfield viscosity (100/min): 1,300 mPa · s pH value: 8.5

[0110] 4. Cardboard

[0111] 4.1 Cardboard Double Coating

[0112] 4.1.1 Cardboard Precoating

[0113] 100 parts by weight of commercially available CaCO₃ (type 75)

[0114] 3 parts by weight of commercially available starch (native,oxidized, corn or potato starch)

[0115] 14 parts by weight of commercially available latex (XSB)

[0116] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0117] 0.5 parts by weight of commercially available brightener (opt.)solids content: 66% Brookfield viscosity (100/min): 1,000 mPa · s pHvalue: 9.0

[0118] 4.1.2 Cardboard Top Coating

[0119] 50 parts by weight of commercially available CaCO₃ (type 90)

[0120] 50 parts by weight of commercially available clay (fine/Engl.clay)

[0121] 13 parts by weight of commercially available latex (acrylate)

[0122] 2 parts by weight of commercially available co-binder (acrylate)

[0123] 0.8 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0124] 0.6 parts by weight of commercially available Ca stearate solidscontent: 60% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 8.5

[0125] 5. Special Papers

[0126] 5.1. Labels

[0127] 70 parts by weight of commercially available clay (normal/Engl.clay)

[0128] 10 parts by weight of commercially available TiO₂ (rutile)

[0129] 20 parts by weight of commercially available CaCO₃ (type 90)

[0130] 16 parts by weight of commercially available latex (XSB)

[0131] 0.5 parts by weight of commercially available hardener (EH)(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0132] 0.6 parts by weight of commercially available Ca stearate solidscontent: 60% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 8.5

[0133] 5.2 Flexible Packing

[0134] 80 parts by weight of commercially available clay (normal, Engl.clay)

[0135] 20 parts by weight of commercially available CaCO₃ (type 90)

[0136] 14 parts by weight of commercially available latex (acrylate)

[0137] 0.8 parts by weight of commercially available CMC

[0138] 0.5 parts by weight of commercially available hardener(urea-formaldehyde, melamine-formaldehyde, epoxy resin)

[0139] 0.6 parts by weight of commercially available brightener (opt.)

[0140] 1.0 parts by weight of commercially available Ca stearate solidscontent: 58% Brookfield viscosity (100/min): 1,200 mPa · s pH value: 8.5

EXAMPLE

[0141] Cleaner rejects from the process of a commercially availablepapermaking machine of the prior art were milled in a 15% by weightsuspension to a slurry having a grain size of <10 μm and added to thestock flow of the paper stock.

[0142] Shortly after the connecting of the milling installation with thecleaner rejects milled according to the invention, an increase of theashes content in the paper could be established.

[0143] The ashes content increased, and the dosage of filler could beconsequently reduced. From the milling installation, about 16 to 18l/min of pigment slurry consisting of milled cleaner rejects wassupplied to the pulp chest. To maintain the ashes content on thepredetermined constant level, the usual dosage of fresh filler could bereduced from 10 l/h to 6.0 l/h.

[0144] In the covered period, the milling installation ran withouttrouble. The ashes content of the stock flow varied to the usual extent.The retention slightly decreased initially, but increased to the usualvalues in the course of the experiment. The amount saved was about 240l/h of fresh pigment slurry.

[0145] The test run over about 10 hours showed that the processedcleaner rejects can be employed again as a filler in the stock by theprocess according to the invention without retention loss.

[0146] Statements relating to the composition of the cleaner rejectslurries: solids content: about 24.0% pigment proportion: about 85.0%,based on the solids content fiber proportion: about 15.0%, based on thesolids content

1. A process for recycling solid cleaner rejects from the preparation ofpaper, paperboard and cardboard, especially from centrifugal cleanersfrom the preparation of paper, paperboard and cardboard, characterizedin that cleaner rejects, which contain fibers, coating pigments and/orfillers, are milled to the desired grain size distribution, optionallywith the addition of water, coating pigment, fresh filler and/or fillerslurry, and employed as a raw material for the paper stock and/orcoating slurry.
 2. The process according to claim 1, characterized inthat the separation of the cleaner rejects is effected by flocculationand sedimentation, filtering, screening and/or centrifuging.
 3. Theprocess according to claim 1, characterized in that cleaner rejectshaving a concentration of fillers and/or coating pigments in an amountof from 1 to 99% by weight, especially from 30 to 70% by weight, basedon the solids content, are employed.
 4. The process according to claim3, characterized in that cleaner rejects having a concentration offibers in an amount of from 1 to 99% by weight, especially from 30 to70% by weight, based on the solids content, are employed.
 5. The processaccording to one or more of claims 1 to 4, characterized in that saidcleaner rejects are milled in the presence of from 1 to 1000% by weight,especially from 100 to 1000% by weight, of water, based on the solidscontent.
 6. The process according to one or more of claims 1 to 4,characterized in that usual milling aids and/or dispersing aids areadded to a slurry having a solids content of from 30 to 85% by weight,especially from 40 to 75% by weight.
 7. The process according to any ofclaims 1 to 6, characterized in that usual milling aids and/ordispersing aids are added in an amount of from 1 to 100% by weight,based on the cleaner rejects.
 8. The process according to one or more ofclaims 1 to 7, characterized in that cleaner rejects are milled to aslurry or powder having a grain size distribution of from 10 to 99% byweight of particles <1 μm, especially from 10 to 95% by weight ofparticles <1 μm, respectively based on the equivalent diameter.
 9. Theprocess according to one or more of claims 1 to 8, characterized in thatcleaner rejects are milled to a powder and/or slurry having a grain sizedistribution of a) from 95 to 100% by weight of particles <10 μm; b)from 50 to 100% by weight of particles <2 μm, especially from 50 to 95%by weight of particles <2 μm; c) from 27 to 95% by weight of particles<1 μm, especially from 27 to 75% by weight of particles <1 μm; and d)from 0.1 to 55% by weight of particles <0.2 μm, especially from 0.1 to35% by weight of particles <0.2 μm; respectively based on the equivalentdiameter of the particles.
 10. The process according to one or more ofclaims 1 to 9, characterized in that the milling of the cleaner rejectsis performed in a dry mill or wet mill, especially in a verticalagitator ball mill.
 11. Use of a cleaner reject slurry according to oneor more of the preceding claims for the preparation of a precoatingslurry for the paper industry, especially of coating slurries forvarious segments, such as sheet-fed offset, rotary offset, intaglioprinting, cardboard and special papers.
 12. Use of cleaner rejects as aslurry or powder according to any of claims 1 to 10 to be employed inthe stock in papermaking.